Path: csiph.com!x330-a1.tempe.blueboxinc.net!usenet.pasdenom.info!aioe.org!feeder.news-service.com!newsfeed.xs4all.nl!newsfeed6.news.xs4all.nl!xs4all!newsgate.cistron.nl!newsgate.news.xs4all.nl!post.news.xs4all.nl!not-for-mail Return-Path: X-Original-To: python-list@python.org Delivered-To: python-list@mail.python.org X-Spam-Status: OK 0.005 X-Spam-Evidence: '*H*': 0.99; '*S*': 0.00; 'mentioned,': 0.04; 'received:edu.au': 0.07; 'silently': 0.09; 'wrote:': 0.15; 'billy': 0.16; 'chmod': 0.16; 'fiddle': 0.16; 'from:addr:cs': 0.16; 'from:addr:zip.com.au': 0.16; 'from:name:cameron simpson': 0.16; 'message-id:@cskk.homeip.net': 0.16; 'mkdir': 0.16; 'received:202.125.174': 0.16; 'received:202.125.174.133': 0.16; 'received:boardofstudies.nsw.edu.au': 0.16; 'received:cskk.homeip.net': 0.16; 'received:harvey.boardofstudies.nsw.edu.au': 0.16; 'received:homeip.net': 0.16; 'received:nsw.edu.au': 0.16; 'cc:addr :python-list': 0.16; 'question.': 0.16; 'exists': 0.19; 'cheers,': 0.19; 'cc:2**0': 0.21; 'cc:no real name:2**0': 0.22; "doesn't": 0.22; 'header:In-Reply-To:1': 0.22; 'ken': 0.23; 'locking': 0.23; 'once.': 0.23; 'xml': 0.25; 'up.': 0.26; '(and': 0.27; 'cc:addr:python.org': 0.30; 'lock': 0.30; 'this.': 0.31; "won't": 0.32; 'it.': 0.33; 'header:User-Agent:1': 0.34; 'there': 0.34; "can't": 0.34; 'doc': 0.35; 'charset:us-ascii': 0.36; 'file': 0.36; 'received:au': 0.36; 'drives': 0.37; 'but': 0.37; 'could': 0.37; 'using': 0.37; 'another': 0.38; 'subject:: ': 0.38; 'george': 0.38; 'two': 0.38; 'put': 0.38; 'either': 0.39; 'might': 0.39; 'plain': 0.40; 'give': 0.60; 'your': 0.60; 'happen': 0.62; 'received:202': 0.66; 'cameron': 0.67; 'subject:program': 0.67; 'habit': 0.84; 'nfs': 0.84; 'problematic': 0.84; 'dream': 0.97 Date: Sat, 16 Jul 2011 08:37:41 +1000 From: Cameron Simpson To: Billy Mays <81282ed9a88799d21e77957df2d84bd6514d9af6@myhashismyemail.com> Subject: Re: Looking for general advice on complex program MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.20 (2009-06-14) References: Cc: python-list@python.org X-BeenThere: python-list@python.org X-Mailman-Version: 2.1.12 Precedence: list List-Id: General discussion list for the Python programming language List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Newsgroups: comp.lang.python Message-ID: Lines: 26 NNTP-Posting-Host: 2001:888:2000:d::a6 X-Trace: 1310769466 news.xs4all.nl 23982 [2001:888:2000:d::a6]:60470 X-Complaints-To: abuse@xs4all.nl Xref: x330-a1.tempe.blueboxinc.net comp.lang.python:9576 On 15Jul2011 16:03, Billy Mays <81282ed9a88799d21e77957df2d84bd6514d9af6@myhashismyemail.com> wrote: | I remember reading that file locking doesn't work on network mounted | drives (specifically nfs mounts), but you might be able to simply | create a 'lock' (mydoc.xml.lock or the like) file for the XML doc in | question. If that file exists you could either hang or silently | give up. Not sure if that helps. There are two approaches to this. Plain old make-a-file won't work - it is racy (and as mentioned, you can't rely on the various lock facilities). You can create a file while your umask is 0777; it will be non-writable immediately (no chmod required), preventing another attempt to make it. My personal habit is to make a directory for the lock; mkdir also can't happen twice to the same name, you don't need to fiddle you umask (racy and annoying, and problematic if you're using multiple threads), _and_ you can put meta info inside it, like pid files etc. Cheers, -- Cameron Simpson DoD#743 http://www.cskk.ezoshosting.com/cs/ I had a wierd dream with Ken Thompson in it once. - George Politis